Teaching modes of traditional teaching ways are becoming increasingly inadequate to the needs of education development. Due to site constraints and non-repeatability of classes, there generally exist the following shortcomings: an order problem of students' seats leads to that students seated at the back cannot see contents of the blackboard or projections; and students can only review notes after class and cannot replay the classes.
In view of the traditional teaching ways, the basic way of the network teaching method existed is: storing the prerecorded audio and/or video information of teachers in a user terminal; and correspondingly uploading the information to the server of a network teaching platform system for students to correspondingly read the information for studies. Through such method, each student can get an equal lesson-taking feeling, as well as a channel of replaying the classes after class at any time.
In such network teaching method, content displayed on the teacher user terminal and content or operations showed by the teacher require to be synchronously transmitted to the student user terminal through the network, so as to achieve sharing of screen displaying information.
The first reference (“Journal of Image and Graphics”, Volume 8, Issue 9, September 2003, Zhang Liping et al., “Screen Sharing Scheme Based on Copying Screen and Data Compression”) discloses that common screen sharing includes two ways: one achieved by using Graphical User Interface (GUI) vector instructions at the bottom of an operation system; and screen sharing is achieved by utilizing copying screen and a compression technology, where screen displaying content is not achieved by being broken into specific drawing commands, but reappearing of copying screen content is achieved by copying the screen image first, and then performing data compression processing and transmitting it to a client, and decoding, by the client, to display it.
It could be seen that the existing network teaching system generally includes: a teaching information supply terminal (a teacher user terminal), a teaching information receiving terminal (a student user terminal), a server (a local server or a remote background server), a teaching equipment (such as an electronic whiteboard and a projection apparatus), and a wired or wireless interconnection network. These terminals are mainly desktop electronic computers, and adopted networks are generally wired networks based on network cables, which results in that teaching equipment need to be installed in advance, but it is not easy to be moved after the installation. As staffs involved in teaching and learning, they cannot take away terminals they use, and it is not convenient to use the terminals again after completion of the teaching process, for example, it is not convenient for students to review.
There still exist the following problems in the existing network teaching system when processing image synchronous displaying: the student user terminal receives the same screen data in a slow speed; and the teaching process is not smooth with buffering phenomena. That is because in the process during which the existing network teaching system transmits the same screen data, ways of video streaming and teachers manually intercepting screens according to their own judgements are mostly used, which results in when there is an excessive number of student user terminals, a large amount of data needs to be transmitted; and a slow speed, unsmooth displaying, and a buffering phenomenon often appearing in multiple concurrent network transmission affect students' class experience. Besides, teachers need to consider performing timely screen-interception operations while lecturing. Sometimes teachers may forget to intercept screens to send to students, while students cannot determine whether they acquire timely screenshot images, which affects teaching results.
In recent years, in order to facilitate the network transmission of image data and improve the transmission efficiency and fluency, a lot of image compression algorithms emerge, not only making image file storage save plenty of room, but also making the network transmission faster and more efficient. There are generally two kinds of image format compression types, namely, lossy compression and lossless compression. Many compression standards of images and videos use Discrete Cosine Transform (DCT) transform such as Joint Photographic Experts Group (JPEG) and Moving Picture Experts Group (MPEG.).
The second reference (“Modern Computer”, 2006, No. 5, Huang Fan, “JPEG Image Retrieval Technique Based on Compressed Fields”) discloses an image compression method. As shown in FIG. 1, a JPEG lossy compression coding step based on the DCT transform generally includes: first, dividing an image into several blocks of 8×8 matrices, where each block consists of one direct current eigenvalue (DC eigenvalue) and 63 alternating current eigenvalues (AC eigenvalues); second, performing forward DCT transform to transform a spatial domain into a frequency domain for expression so as to concentrate capabilities on a handful of eigenvalues; third, performing lossy quantization on DCT frequency eigenvalues according to a quantization table to eliminate visual redundancy; fourth, sorting the quantized eigenvalues in a “Z” shape to form a one-dimensional eigenvalue sequence; fifth, encoding the DC eigenvalue by using Differential Pulse Code Modulation (DPCM) algorithm, while performing lossless compression on the AC eigenvalue by using Run Length Encoding (RLE); and finally, performing Huffman encoding on the DC and AC eigenvalues after the processing. Representing texture features and pixel values of each block in the image, the DC eigenvalue and the AC eigenvalue are the main elements that form the image. However, in the existing solution, image acquisition such as copying screen (or intercepting screen), is performed either manually or by setting automatic screenshot according to time for transmission. But problems that whether the screenshots message transmitted is duplicated or effective all exist. Transmissions of unnecessary or repeated images may increase network transmission burden and may also affect users' experience.
In the network teaching process, in order to simulate the same effect as the actual teaching ways and improve quality of online teaching, it is required to promptly same-screen display electronic blackboard-writing and other teaching content displayed on the teacher user terminal on the student user terminal, which requires more efficient and intelligent acquisition, compression, and transmission of images and operation instructions as well as a corresponding network teaching method and system.